The group type sync has to be disabled in any case:
connector/s4/mapping/group/grouptype=false
I've changed the wiki article. The group sync can be activated later via Bug #32863
I've also added the dbcheck command on the first system after the migration.
The sambaGroupType rewrite have been removed from the classicupdate code in setup-s4.sh.

nop, another problem
samba4 demotes the other (samba3) dc's
Demoting BDC account trust for pbackup, this DC must be elevated to an AD DC using 'samba-tool domain dcpromo'^M
Demoting BDC account trust for pslave, this DC must be elevated to an AD DC using 'samba-tool domain dcpromo'^M
this leads to a password mismatch between ldap and machine.secret on the dc backup